Embed Size (px)
Citation preview
Aalborg Universitet
Experimental testing of two solar panel simulations
Ritchie, Andrew Ewen; Leban, Krisztina Monika; Raducu, George-Alin
Published in:Scientific Bulletin of the "Politehnica" University of Timisoara, Transaction on Power Engineering
Publication date:2008
Document VersionPublisher's PDF, also known as Version of record
Link to publication from Aalborg University
Citation for published version (APA):Ritchie, E., Leban, K. M., & Raducu, G-A. (2008). Experimental testing of two solar panel simulations. InScientific Bulletin of the "Politehnica" University of Timisoara, Transaction on Power Engineering "Politehnica"University of Timisoara.
General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.
? Users may download and print one copy of any publication from the public portal for the purpose of private study or research. ? You may not further distribute the material or use it for any profit-making activity or commercial gain ? You may freely distribute the URL identifying the publication in the public portal ?
Take down policyIf you believe that this document breaches copyright please contact us at [email protected] providing details, and we will remove access tothe work immediately and investigate your claim.
Downloaded from vbn.aau.dk on: maj 31, 2018
EXPERIMENTAL TESTING OF TWO SOLAR PANEL SIMULATIONS
Krisztina Leban Institute of Energy Technology, Aalborg University, Pontoppidanstræde 101, Aalborg, Denmark,
Alin Argeseanu Polytechnic University of Timisoara, Department of MAUE, Timisoara, Romania
Ewen Ritchie Institute of Energy Technology, Aalborg University, Pontoppidanstræde 101, Aalborg, Denmark, [email protected]
Abstract. This paper focuses on verifying two simulation models by
experimental [1]. Two models for silicon polycrystalline photovoltaic solar cells [2], [3] were analysed. Comparison between the Power vs. Voltage and Current vs. Voltage curves obtained from the simulation to those obtained experimentally was made.
The goal is to identify if a simulation model gives correct information about the behaviour of one single solar panel for varying temperature and irradiance. Final validation was done by comparing experimental and simulation results. The single panel model was integrated into array of 16 elements. This can be used a simulation of an isolated micro grid or in a hybrid energy system [4], [5].
By comparing simulation results from both models with experimental results, we can conclude that model 2 is the most reliable one.
Key words: photovoltaic, solar cells, renewable energy,
simulation, model.
1. Introduction Solar cells are a renewable, non-polluting source of energy
that are increasingly used for hybrid (solar panels and grid) or stand-alone applications [4], [5] and [6]. In order to have an idea about the performance and behaviour of the solar micro-grid, a simulation model of the photovoltaic array should de made. For this purpose, the simulation of a single solar cell must give accurate information of the output voltage with respect to the inputted ambient temperature and irradiance.
To determine the characteristics of the solar cell, the power vs. voltage (PV) and current vs. voltage (IV) curves must be constructed. Current is measured at the output when the cell is short-circuited [7]. From these curves the maximum power point (MPP) can be ascertained [8].
Data sheet values specify typical PV and IV curves obtained under standard test conditions, STC (ambient temperature of 25 °C and irradiance of 1000 W·m−2) [3].
The goal of this work is to identify if the simulation models give correct information about the behaviour of a single solar panel for varying temperature and irradiance. Models were validated by comparing experimental and simulation results. The single panel model was integrated into an array of 16 elements. As an example, this may be useful in the simulation of an isolated micro grid or in a hybrid energy system [4], [5].
In addition to comparing simulation results with experimental results, the implemented models were tested by observing the response to standard test condition input values. Both simulated models were tuned using datasheet values and measured standard test condition values for temperature and irradiance.
2. Photovoltaic panel models
2.1. First PV Model The equivalent circuit of the first model proposed by Altas,
and Sharaf, [2] is presented in Figure 1. The solar cell is modelled as a current source. Iph, the
photovoltaic current is proportional to the ambient irradiance level and to the temperature of the panel. To allow for losses, a series (Rs) and parallel resistance (Rp) are commonly included in the circuit. In this model, the parallel resistance was neglected in order to simplify the model [2], [3].
The diode, D represents the PN junction of the PV solar cells with I0 reverse saturation current of the diode [2].
Figure 1: PV Model 1 – Solar panel equivalent circuit
1
The output voltage of the PV panel is given by:
The curve fitting factor, A, was adjusted so that at rated
input values of temperature and irradiance the datasheet values of output were obtained as model outputs. The same approach was taken to obtain the temperature and irradiance correction coefficients. In this way, the model was tuned to give the datasheet values at STC(equations (2) to (4)).
Correction coefficients used to adjust the voltage Vc and current Iph for various values of ambient temperature and irradiance are as follows:
• Temperature correction factors for voltage and current respectively:
)TTc(1C xTTV −β+= (2)
)TT(S
1C xCTC
TTI −β
γ+= (3)
• Irradiance correction factors for voltage and current
respectively:
• Applying the correction factors to Iph and Vc the
temperature-irradiance relationship was obtained.
SVTVccx CCVV = (6)
SITIphphx CCII = (7)
where: Vc - cell output voltage - [ V ] A- curve fitting factor [ - ] k - Boltzmann constant [J/K] e - electron charge [C] Tc- STC temperature [ K ] Tx- ambient temperature [ K ] Sc- STC irradiance [W/m2 ] Sx- variable irradiance [W/m2 ] Iph- photocurrent [A] I0- reverse saturation current of the diode [A] Rs - series resistance of one cell [Ω] CTV - temperature voltage correction factor [-]
CTI - temperature current correction factor [-] CSV - irradiance voltage correction factor [-] CSI - irradiance current correction factor [-] βT - correction coefficient [1/K] γT - correction coefficient [W/Km2 ] αs - slope of change in the cell operating temperature due to
a change in the solar irradiation level [Km2 /W]
2.2. Second PV Model The second model to be studied, proposed by Sera,
Teodorescu, and Rodriguez, [3], requires active compensation (at every moment) of Rs, Vc, and Iph ((10) to (19)) as functions of temperature and irradiance. The equivalent circuit for this model is that of Figure 1. In [3] the effect of the shunt resistor was considered, but in order to obtain a valid comparison between models 1 and 2, this was not done in this paper.
• Thermal voltage for variable temperature Tx:
enkTAV cxD
t =
(8)
• Diode ideality factor:
( )e
VIIA mppscmpp
D
−−=
(9
• Series resistance calculation using datasheet values:
)
• Open circuit voltage :
t
.
o
scoc V
IIlnV ⎟⎟
⎠
⎞⎜⎜⎝
⎛=
(11)
• Temperature dependence of voltage:
( )cxvococT TTkVV −+=
(12)
• The short-circuit current and photo-current
were considered to be proportional to the value of irradiation.
x
x
SS
phphG
scscG
IIII
==
(13)
• Dark saturation current:
0.001ee
IIt
socT
t
ocV
RIV
VscT
o
−+−
−= (14)
cs0
c0phcC IR
IIII
lne
AkTV −⎟⎟⎠
⎞⎜⎜⎝
⎛ −+= (1)
)SS(1C CxTTSV −αβ+= (4)
)S(SS11C CxC
SI −+= (5)
( ) I
V I V
I I I
I Iln V
Roc
mpp
mppscmpp
sc
scmmpmmp
S
+−⎟⎟⎠
⎞⎜⎜⎝
⎛ +−−
= mpp
(10
)
2
• The output voltage of the PV panel, compensated for irradiance and temperature :
I
eIeIeIlnRI
Vsc
VV
scVRI
xVV
xsx
x
t
oc
t
ssc
t
oc
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛−−−+−
=
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛
(15)
The influence of irradiance is modelled indirectly by (14) and (17) introduced into (16).
Equations were implemented in MATLAB script language. Vmpp-voltage at the Maximum Power Point (MPP) in STC Voc - open-circuit voltage in STC [ V ] VocT - open circuit voltage as a function of temperature [V] Vt - junction thermal voltage [V] Vx - PV voltage (with T and S) [V ] Impp - current at the MPP in STC [ A] Isc - short-circuit current in STC [A ] Io - dark saturation current [A ] Ix - PV current (with T and S) [A] Ic - cell output current [A] IocT - short-circuit current as a function of temperature [A] AD - diode ideality factor [-] nc - number of panels in the array [-] ns - number of cells in the panel connected in series [-] ki - temperature coefficient of the short-circuit current [-] kv - temperature coefficient of the open-circuit voltage [-]
3. PV simulation Models 1 and 2 were implemented and simulated in
MATLAB-Simulink.[9] ,[10]. An array of 16 cells was studied using the two models. Results from the two simulations were compared to each other and to experimental measurements.
Figure 2: PV Model – Simulation System Block Inputs and outputs (Figure 2) to the two models were the
same:
4. a current ramp Ic (varying from zero to the data sheet short circuit to simulate the varying current of the panel)
5. Tx-the variable ambient temperature 6. Sx- the variable irradiance 7. single panel and array output voltage. Care was taken to avoid windup effects caused by the Ic ramp signal block [10].
Simulation results from the first model are presented in
Figures 3 a and 3 b. STC curves are displayed using thicker lines. Various temperature and irradiance values were applied.
The same approach was taken to model 2. The results can be viewed in Figures 4, 5 and 6.
It may be observed, that with rising temperature, the output
voltage of the panel, and implicitly the output power, decreases. The value of the current is not greatly affected by changes of temperature.
Irradiance lower than STC irradiance causes the output voltage, current and power to fall.
4. Experiments
4.1 Experimental layout Experiments were carried out on two arrays of eight
polycrystalline solar panels connected in series ( Figures 5 and 7).
Five sets of measurements were made at 20 minutes intervals. The results are presented in Figures 8 and 9.
For measurements a model PVPM 1000C meter and a PVPM_LST1000 protection switch were used. With this device the photovoltaic voltage, current and power may be measured.
Figure 7: Experimental Arrangement
xscT.
x SII = (16)
3
a b
Figure 3: PV Model 1 – One cell PV and IV simulated curves at variable temperature (a) and irradiance (b)
a b
Figure 4: PV Model 2 – One cell PV and IV simulated curves at variable temperature (a) and irradiance (b)
4
Figure 5: PV Model 2 – Series connection-simulation
a b
Figure 6: PV Model 2 – Series array simulation curves at variable temperature (a) and irradiance (b)
5
4.2 Experimental results Measured PV and IV curves were recorded at 19.5°C
and 695 W/cm2 are presented in Figure 8. In Figure 9 experimental IV curves for ambient temperatures between 25.2 and 28 °C and for irradiance between 635 and 693 W/cm2 are shown.
Figure 8: Experimental IV and PV Curves
Figure 9: Temperature and irradiance variation curves (experimental results)
6
5. Discussion of results Since temperature curves given by both models are
similar in shape, the irradiance curves must be studied in detail. The information needed from the simulation is the voltage variation with irradiance.
As may be seen from Figure 9, the shapes of the curves prove that model 1 does not output valid information at variable ambient irradiance (Figure 3). Reason for this lies in the compensation method used in [2]. Also correction coefficients α T, β T and γT could not be assigned precise values due to their empiric origins.
Actively compensating equivalent circuit parameters
of model 2 make a more reliable output than model 1. In the time that the test where carried out (~2 hours),
ambient temperature remained approximately constant, irradiance however varied so curves from Figure 8 can be considered irradiance curves. Variation of panel voltage was under 10V. This fact was reflected by model 2, but not by model 1.
I. CONCLUSIONS By comparing simulation results from both models
with experimental results we can conclude that model 2 is the most reliable one. Model 1 has a correct varying input temperature response, but irradiation dependences could not be correctly set. In the preferred model, active compensation of parameters has made the simulation less susceptible for errors.
ACKNOWLEDGEMENTS We wish to thank group members Adelina Agap,
Adrian Constantin, Madalina Cristina Dragan, Borja, Imanol Markinez Iurre and, Marcos Rupérez Cerqueda for their contribution in the experimental part of the project.
REFERENCES
[1] Residential micro-grid system, 7th semester project – January 2008, Institute of Energy Technology, Aalborg University, Aalborg Denmark Adelina Agap, Adrian Constantin, Madalina Cristina Dragan, Borja, Imanol Markinez Iurre, Krisztina Leban, Marcos Rupérez Cerqueda
[2] A Photovoltaic Array Simulation Model for Matlab-Simulink
GUI Environment Altas, I. H.; Sharaf, A.M.; Clean Electrical Power, 2007. ICCEP '07. International Conference on 21-23 May 2007 Page(s):341 - 345
[3] PV panel model based on datasheet values Sera, Dezso;
Teodorescu, Remus; Rodriguez, Pedro; Industrial Electronics, June 2007. ISIE 2007 ISBN: 978-1-4244-0755-2
[4] A new solar energy conversion scheme implemented using
grid-tied single phase inverter Mekhilef, S.; Rahim, N.A.; Omar, A.M.; TENCON 2000. Proceedings, September 2000, ISBN: 0-7803-6355-8
[5] A standalone photovoltaic (AC) scheme for village electricity
A.M. Sharaf', SM IEEE, A.R.N.M. Reaz UI Haque, Jan. 2005, ISSN: 0160-8371, ISBN: 0-7803-8707-4
[6] Models for a standalone PV system
Anca D Hansen, Poul Sørensen, Lars H. Hansen, Henrik Binder, Risø-R-1219(EN)/SEC-R-12 Risø National Laboratory, December 2000, 77 p., ISBN 87-550-2776-8
[7] PVPM1000C Peak Power Measuring Device for PV-Modules
PV-Engineering GmbH Users Manual 2004 [8] A Variable Step Maximum Power Point Tracking Method
Using Differential Equation Solution Luo, Fang; Xu, Pengwei; Kang, Yong; Duan, Shangxu; Industrial Electronics and Applications, 2007. ICIEA 2007. 2nd IEEE Conference on 23-25 May 2007 Page(s):2259 - 2263
[9] Dynamic Simulation of electric Machinery Using MatLab
Simulink Chee-Mun Ong; Prentice Hall PTR 1998 ISBN 0-13-723785-5
[10] Feedback Control of Dynamic Systems fourth edition Gene
Franklin, David Powel, Abbas Emami – Naeini, Prentice Hall 2002 ISBN 0-13-098041-2
7
